The invention relates to a tool for final machining of a valve seat and valve guide in a cylinder head of a combustion engine. The invention also relates to a method for final machining of a valve seat and valve guide in a cylinder head of a combustion engine.
Tools and methods for final machining of a valve seat and valve guide are known. This kind of machining involves one of the most exacting machining in the cylinder head. In particular, the coaxiality of the valve seat and the valve bore is a criterion for the tightness and thus the fuel consumption of the combustion engine. Different methods exist for attaining the required precision which usually is in the range of 0.025 mm maximum.
For the machining of a valve seat and valve guide on a machining center, the known methods require at least two tools, and for very small diameters even three tools, depending on the diameter of the valve guide. With the aid of a tool, a pilot bore is prepared in which the subsequently inserted final machining tool moves during the cutting. The machining time in this case is relatively long because it is necessary first to prepare a pilot bore before the final machining can be done.
Another method is carried out on transfer lines. To achieve the rigidity required for the tool used for machining the valve guide, a feed-out spindle comprising two tools is employed. In this case, a thin tool intended for the valve guide is moveable within another tool and is guided through a bushing.
It has been established that the machining times on a machining center are too long and that the machining on a transfer line requires very expensive tools in order to achieve the precision needed for the machining of a valve seat and valve guide.
Hence, the object of the invention is to provide a tool and a method for the final machining of a valve seat and valve guide in a cylinder block of a combustion engine that do not have these drawbacks.
To reach this objective, we propose a tool characterized in that between a first section of the tool used for the machining of the valve seat and a second section used for the machining of the valve guide there is provided a separation site comprised of a cone and a conical recess to receive said cone. By means of this separation site, the rigidity of the tool is substantially increased. Moreover, the assembly is much simpler and more economical than with feed-out tools.
Other embodiments of the invention are covered by the subclaims.
To reach the said objective, we also propose a method for the final machining of a valve seat and valve guide in a cylinder block of a combustion engine. The method is characterized in that the final machining is performed with a single tool. In other words, it is not necessary to create a pilot bore for the final machining using a preliminary machining tool. Also, no guide bushing is needed for the final machining.
A preferred embodiment of the method of the invention is characterized in that the final machining is carried out in a single step. In other words, creating a valve seat and valve guide in a cylinder block does not require a preliminary as well as a final machining.